As far as I remember there were grey uniforms or clothing in the last film (I seem to recall the shuttle officer in grey, as well as Pike during the bar scene) so it wouldn't appear inconsistent with last time.
Call me old fashioned but I rather like the notion that hats/caps are still attached to a future service's more formal uniforms. I think it finishes off a service uniform nicely. Anachronistic, sure, but better than skants and one piece's that don't smuggle the budgie.
'If the Apocalypse starts, beep me!' - Buffy Summers
'The sky's the limit.....' Jean-Luc Picard, 'All Good Things'
courtesy of Saquist